As bosk said, no one knows for sure. However, JP penned the entire storyline, map, characters, etc., and came up with the idea on his own. He took a solid year to create this concept, according to his Rolling Stones interview. It's my guess that he also to sole responsibility of the lyrics, with possibly some input from the rest of the guys. But the bulk of the lyrics were on him, with just some tweaks here and ther.